1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and more specifically to an active matrix liquid crystal display apparatus configured to control a number of pixel electrodes in a liquid crystal display panel on the basis of a RGB signal (a red signal, a green signal and a blue signal which constitute a trichromatic signal).
2. Description of Related Art
A conventional active matrix liquid crystal display apparatus has been constructed to receive a red signal, a green signal and a blue signal and to drive analog or digital driver circuits for the purpose of controlling the pixel electrodes in a liquid crystal display panel.
Referring to FIG. 1, there is shown a block diagram illustrating one example of a conventional active matrix liquid crystal display apparatus. The shown conventional active matrix liquid crystal display apparatus includes an A/D converter (analog-to-digital converter) 18 receiving a red signal R, a green signal G and a blue signal B for converting them into digital signals N11, and a controller 4A receiving a horizontal synchronizing signal HS and a vertical synchronizing signal VS for controlling various parts of the active matrix liquid crystal display apparatus. The controller 4A includes therein a gamma (.gamma.) conversion circuit 2 receiving the digital signals N11 for generating output signals N12.
The active matrix liquid crystal display apparatus also includes a D/A converter (digital-to-analog converter) 19 for converting into analog signals N13 the output signals N12 obtained by converting the output signals N11 of the D/A converter 18 by the gamma (.gamma.) conversion circuit 2, a data inverting circuit 3 receiving the analog signals N13 for generating complementary data signals N14 and N15, and a low-pass filter (LPF) 5 and a voltage controller oscillator (VCO) 6 associated to the controller 4A.
An LCD (liquid crystal display) panel 9 includes a number of pixel electrodes 13 located in the form of a matrix. In FIG. 1, only two pixel electrodes are shown for simplification of the drawing. This LCD panel 9 is associated with an upper side horizontal driver circuit 11 and a lower side horizontal driver circuit 12 which are driven by the complementary data signals N14 and N15 outputted from the data inverting circuit 3 through signal buses 7 and 8, respectively, for the purpose of controlling a potential in a horizontal direction of the LCD panel 9. The LCD panel 9 is also associated with a vertical driver circuit 10 controlled by the controller 4A for controlling a potential in a vertical direction of the LCD panel 9.
In the above mentioned circuit, the ted signal R, the green signal G and the blue signal B are converted by the A/D converter 18 into the digital signals N11, which are in turn gamma-converted into the digital signals N12 by use of a ROM (read only memory) which is provided within the gamma (.gamma.) conversion circuit 2 and which stores a brightness-voltage characteristics of the LCD panel 9 and input-output conversion codes necessary for demodulating a video signal (which has been raised to 0.45 power). Then, the gamma-converted digital signals N12 are returned to the analog signals N13 by the D/A converter 19, and the analog signals N13 are sign-converted so that the complementary analog signals N14 and N15 are generated. These complementary analog signals N14 and N15 are supplied to the upper side horizontal driver circuit 11 and the lower side horizontal driver circuit 12 (both of the analog type horizontal driver) which are provided at an upper side and at a lower side of the LCD panel 9. The above apparatus is an analog type active matrix liquid crystal display apparatus.
The above mentioned conventional analog type active matrix liquid crystal display apparatus requires six or eight bits or more for each output signal of the A/D converter, because of recent inclination of a full color display of the liquid crystal display. In addition, because of an increased number of pixels in the LCD panel, the dot clock of the video signal is apt to be increased. For example, in the LCD panel on the order of 1,300,000 pixels, the A/D converter requires a sampling rate of 100 MHz or more. In the A/D converter having the bit precision on the order of 8 bits and the sampling rate of 100 MHz or more, a power consumption is as large as 0.5 W to 1 W. Furthermore, the size of an overall apparatus becomes large, and the cost correspondingly becomes high. Accordingly, the active matrix liquid crystal display apparatus using the A/D converter is disadvantageous in that a low power consumption (that is a merit of the LCD panel) cannot be effectively exerted, and the whole of the apparatus is large in size and expensive.
In the above mentioned conventional analog type active matrix liquid crystal display apparatus, furthermore, the D/A converter used after the gamma conversion are also required to have a high bit precision and the high speed operation, similarly to the A/D converter used before the gamma conversion. This further increases the power consumption and makes the whole of the apparatus large in size and expensive.
Now, referring to FIG. 2, there is shown a conventional digital type active matrix liquid crystal display apparatus. The shown digital type active matrix liquid crystal display apparatus includes an A/D converter 18 receiving a red signal R, a green signal G and a blue signal B for converting them into digital data signals N11A and N11B, and an upper side horizontal driver circuit 11A and a lower side horizontal driver circuit 12B which receive the digital data signals N11A and N11B, through signal buses 7A and 8A, respectively, and a gray scale voltage supply 20 for supplying a gray scale voltage to the upper side horizontal driver circuit 11A and the lower side horizontal driver circuit 12B, respectively, a controller 4B for controlling a LCD panel 9, a vertical driver circuit 10, the A/D converter 18 and other driver circuits, similarly to the example shown in FIG. 1, and a low-pass filter (LPF) 5 and a voltage controller oscillator (VCO) 6 associated to the controller 4B.
In the shown conventional digital type active matrix liquid crystal display apparatus, the output data signals 11A and 11B are supplied directly to the horizontal driver circuits 11A and 12A, and the gamma conversion is realized by setting the voltage from the gray scale voltage supply 20 to the horizontal driver circuits 11A and 12A.
In the conventional digital type active matrix liquid crystal display apparatus, since it has no D/A converter, the power consumption can be reduced by the amount corresponding to the D/A converter. However, considering each of colors, in the case that a serial-parallel conversion of 1:N is performed in order to meet the precision of six or eight bits or more, or in order to fulfill the operating capability of the peripheral drivers (ordinarily, on the order of 30 MHz), it is necessary to supply the gamma-converted digital signals of 6N bits to 8N bits to the peripheral drivers of the LCD panel. Therefore, a layout or arrangement of wiring conductors becomes very complicated in the conventional digital type active matrix liquid crystal display apparatus. This is a hindrance in miniaturization.